It has long been recognized in the art that fireplace grates merely provide support for one or more logs to raise them above the hearth of a fireplace and that a fireplace is inefficient from the standpoint of utilizing radiant heat from the burning logs. Several different types of andirons or grates have been proposed in the prior art in an attempt to alleviate problems and provide more efficient operation and utilization of the fireplace for heating purposes.
Thus, it is pointed out in U.S. Pat. No. 2,600,753 that the major source of useful heat given off by burning logs in a fireplace is radiant heat emitted by the burning or incandescent logs. Convection cannot play an important part in transfer of heat from a fireplace to a room or other space which is being heated because the draft necessary for operation of the fireplace is from the room into the fireplace and thence upwardly through the flue. It is also pointed out that the hottest, incandescent part of a burning log supported on a grate is the undersurface of the logs. However, it is that precise area that is shielded from direct radiation to a room or other space which is being heated. The grate or andiron disclosed in U.S. Pat. No. 2,600,753 purports to solve this problem by providing andirons which support burning or incandescent logs so as to radiate heat efficiently into a room or other space which it is desired to heat by dividing a bar extending upwardly and outwardly for holding a supply of main logs in an elevated position relative to the hearth of a fireplace and to allow heat from the undersurface of the logs to radiate outwardly from the fireplace, and an auxiliary rod located beneath the upper bar and extending outwardly to support an auxiliary log in a position under the main log to support combustion thereof.
Other proposals to improve the efficiency of fireplaces have included grate type structures for supporting burning fuels such as wood, coal or other solid fuel and having air conveying tubes formed by the grate members for receiving air from the room to be served by the fireplace grate structure, passing the air through the tubes in good heat exchange relation with the burning fuel, and discharging the air back into the room to enhance the heating efficiency. Typical of these structures are those disclosed in U.S. Pat. Nos. 1,030,002, 1,313,085; 1,608,745; and 1,747,259, all of which employ a plurality of hollow tubular members arranged in a generally C-shaped configuration having a lower leg provided with an air inlet to receive air from the room and conduct the same rearwardly, and then upwardly and forwardly about the burning fuel to achieve better heating of the air and then discharge the heated air back into the living space. These devices all rely upon convection currents produced by the heating of the air in the tubular members to draw room air into the lower legs of the tubular members and achieve air circulation movement rearwardly, upwardly, and forwardly through the members to discharge heated air back into the room. The structure disclosed in U.S. Pat. No. 4,018,210 further improved upon the fireplace grate type structures by providing a structure which included a pressurized manifold and associated motor driven fan incorporated in the fireplace grate unit and communicating with the openings at the lower ends of the tubes to distribute pressurized air to the lower inlets of the tubes to be heated during passage through the tubes and discharged in the desired direction back into the room to be heated.
None of the prior art structures are so designed as to give maximum heating and heat radiation efficiency from the fireplace combustion.